On the hand-operated pipettes, in order to be able to adapt the quantity of volume to be pipetted, a device for adjusting this volume is generally provided. By actuating this device, the initial position of the piston is moved, and the pipetting stroke of this piston is therefore modified. More precisely, actuating this adjusting device usually generates the movement of a threaded member which defines a top stop for a control stem, a top end of which carries the control knob, and a bottom end of which cooperates with the piston. So, upon adjusting the volume to be sampled, the axial movement of the threaded member and of its top stop causes, through suitable springs, the simultaneous axial movement of the control stem, the knob and the piston.
The threaded member for adjusting the volume is arranged within a hollow outer body forming a handle, which is intended to be held by the operator's hand when handling the pipette. This hollow outer body is also crossed by the control stem, and further accommodates a counter enabling the value of the adjusted volume to be displayed. This counter includes a plurality of graduated wheels cooperating with the adjusting threaded member, which drives their rotation as this member is actuated during the adjustment. To carry out this driving, gear-type connections are usually fitted between the adjusting threaded member and the wheels of the counter.
The value of the adjusted volume is displayed by means of a window provided on the outer body, this window enabling one of the graduations of each counter wheel to be read. The wheels, for example three wheels, are generally axially stacked and respectively dedicated to indicating the digit of the units, of the tens and of the hundreds. The total value of the adjusted volume is then indicated by axially/vertically reading the three digits appearing through the window laterally provided on the pipette outer body forming a handle.
This design is widely spread on hand-operated pipettes, and is satisfactory. However, there is a need for optimizing the design of the top part of these pipettes, in order to reduce their overall dimensions and/or in order to be able to fit other pipette components without excessively affecting the overall dimensions.
In the prior art, it is known to replace the counter provided with wheels with a digital counter. Nevertheless, this solution can also be improved since it can be affected by reliability issues, and it still requires a large number of components, especially a sensor. Moreover, a power supply of the digital counter is necessary.
The purpose of the invention is therefore to at least partially solve the above-indicated problems, relating to prior art implementations.